The aim of this study was to prepare zopiclone-loaded polycaprolactone microspheres by emulsion solvent evaporation technique with different drug-to-carrier ratios {MP 1 (1:1), MP 2 (1:2), MP 3 (1:3), and MP 4 (1:4)}, characterize and evaluate the in vivo performance. The microspheres were characterized for particle size, surface morphology, drug excipient compatibility, percentage yield, drug entrapment, and in vitro release kinetics. Pharmacokinetics and pharmacodynamics were evaluated after parenteral administration so as to determine the sustained action of the drug after one-time administration of the formulation in a rat model. Of four formulations prepared, MP 2, i.e., 1:2 (drug–polymer) ratio was selected as the optimized formulation based on particle size, particle shape, and the release behavior. The size of microspheres was found to be ranging from 5.4 to 12.1 µm. The shape of microspheres was found to be spherical by SEM. Among the four formulations, MP 2 (1:2) showed maximum percentage yield of 75% ± 2.68%. There was no interaction between drug and polymer by FT-IR study. In the in vitro release study, formulation MP 2 (1:2) showed 86.5% drug release and was found to be sustained for 10 days. The microsphere formulations were able to sustain the release of drug both in vitro and in vivo. Pharmacodynamic study (Maze apparatus) indicated that the anxiolytic activity shown by zopiclone microspheres was significant when compared to the zopiclone solution given daily.
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